Apparatuses and devices installed in a vehicle are electrically controlled by an electronic control device/unit. In recent years, vehicles are highly electrified for high performance and high functionality, resulting in that increasing number of the in-vehicle devices are under control of the Electronic Control unit, or ECU. Therefore, a network bus through which the communications between network nodes are performed is suffering from an ever-increasing communication load among them when the network nodes perform communications according to a control protocol, for the control of the in-vehicle devices.
In addition to achieving high performance and high functionality, safety assurance of the vehicle is also a highly important issue for society. An international standard implemented for a functional safety of the vehicle requires that a vehicle having abnormality is required to transition to a safe state within a preset period of time. In view of such a standard, the network load of the in-vehicle network bus must be appropriately controlled. That is, the vehicle is not enabled to transition to the safe state within the preset period of time in case that the network bus in the vehicle is suffering from an overload communication and is not performing an efficient communication between the network nodes.
For the resolution of the overload communication of the network bus in the vehicle, the network system in a Japanese patent document, JP 2013-239886 A (patent document 1) proposes a changeable payload length of a frame that is exchanged (i.e., sent and received) via the network bus. By changing the payload length of the frame in the network bus, the overload communication of the network bus is lightened, lightening the process load on each of the network nodes, which improves an efficiency of the communications between the network nodes.
In the network system in the above-mentioned patent document 1, in order to determine the payload length of the frame that is exchanged among the network nodes, transmission and reception of the frame are performed according to a dedicated protocol.
That is, each of the network nodes exchanges the frame according to the dedicated protocol that is used exclusively for the determination of the payload length, prior to performing the communications according to the control protocol for the control of the in-vehicle devices.
After determining the payload length, each of the network nodes exchanges the frame with the determined payload length according to the control protocol.
Thus, it is necessary to implement the dedicated protocol that is not normally used for the control of the in-vehicle devices if you use the network system of the above-mentioned patent document 1 for the determination of payload length.
Therefore, in such a network system, the configuration and the control of the network system are complicated. Further, such a network system must interrupt the communications (i.e., the exchange of the frame performed by the control protocol), which leaves a room for improvement in terms of communication efficiency of the network.